1. Field of the Invention
The present invention relates to an imaging apparatus, an image processing apparatus, an image processing system and an image processing method.
2. Description of the Related Art
In conventional digital cameras, there has been known a digital camera provided with a function which directly stores image data yet to be subjected to image processing (which will be referred to as raw data hereinafter) in a recording medium or the like. The raw data is a kind of data obtained by converting an output from an imaging element into a digital image as it is. Therefore, the raw data cannot be viewed or printed as an image if no processing is applied thereto. In that sense, it is assumed that the raw data is subjected to image processing in a dedicated image processing apparatus or a PC application having an image processing function.
Usually, elements (e.g., gradation characteristics, color reproduction, and white balance) concerning image quality when performing image processing in a digital camera are determined at the time of image capturing. Conversion from the raw data into image data subjected to image processing is irreversible. Again changing gradation characteristics, white balance or the like after image processing may lead to a deterioration in image quality as compared with the case where gradation conversion or white balance processing is directly applied to the raw data. On the other hand, when the raw data is subjected to image processing after image capturing, elements concerning an image quality can be freely changed without a deterioration in image quality, and this is recognized as a utility value of the raw data.
Here, the gradation characteristics are determined based on an exposure level when image-capturing raw data and a gradation conversion table when performing gradation conversion. The exposure level is determined when capturing an image. On the other hand, as a technique of determining the gradation conversion table, there have been proposed various techniques, e.g., a technique which uses data stored in an image processing apparatus in advance, a technique which analyzes raw data by an image processing apparatus and generates an appropriate gradation conversion table in accordance with a result of this analysis, a technique which transfers a gradation conversion table attached to raw data to an image processing apparatus, and others. Further, Jpn. Pat. Appln. KOKAI Publication No. 2003-244626 proposes a technique which transfers imaging gamma information indicative of a gamma correction quantity based on imaging characteristics of an imaging apparatus to an image processing apparatus and updates a gradation conversion table previously stored in the image processing apparatus in accordance with output characteristics base on the transferred information.
Furthermore, as conventional digital cameras, one provided with a function which applies image processing and records obtained data in a recording medium or the like is commonly used. Moreover, there has been known a PC application software (a PC application) or the like which reads recorded image data and applies image processing in accordance with preferences of a user. As a content of this image processing, there is, e.g., a change in white balance or in color reproduction. It is preferable that such processing is carried out with respect to data which is linear (γ=1) with respect to a light quantity of a subject rather than data subjected to gradation conversion. Therefore, when performing processing which changes the white balance by a PC application or the like, it is preferable that image data is converted into data which is linear with respect to a light quantity in accordance with inverse characteristics of gradation conversion characteristics applied to the image data and then the white balance or the like is changed, and thereafter gradation conversion is again conducted.
In order to perform such inverse conversion of gradation conversion effected in a camera, characteristics of gradation conversion performed in the camera must be transferred to an image processing apparatus. As techniques which realize this transfer, there have been proposed various techniques such as a technique which previously stores a predetermined gradation conversion table in an image processing apparatus, a technique which transfers a gradation conversion table attached to image data to an image processing apparatus, and others.
Furthermore, the exposure of an image is usually determined at the time of capturing an image. There has been proposed an apparatus provided with a function which demonstrates an effect which is equivalent to the exposure correction in image capturing when raw data is developed. Specifically, a technique which simulates the exposure correction in image capturing by amplifying captured raw data based on a predetermined gain is commonly used.
The exposure correction is generally represented by an exponentiation of 2, and raw data after the exposure correction in each pixel can be calculated by the following expression.Raw data (after exposure correction)=Raw data (before exposure correction)×2 (exposure correction value)
By performing predetermined image processing including gradation conversion to raw data with which exposure correction is simulated, an image closer to an image subjected to exposure correction in image capturing can be obtained.
Moreover, there are a technique which changes an apparent exposure by varying gradation conversion characteristics (more specifically, a gradation conversion table) rather than applying a predetermined gain to raw data like the above expression, a technique which previously stores a plurality of gradation conversion tables in an image processing apparatus, and a technique which transmits a plurality of gradation conversion tables attached to raw data to an image processing apparatus. For example, Jpn. Pat. Appln. KOKAI Publication No. 2003-242163 proposes that image data and its attached information (raw data information, digital exposure correction processing information and others) are created as one file on an image recording apparatus side and processing with respect to the image data is changed based on read information on an information processing apparatus side.